Plasma vs. LCD: Round II

Three years ago, Sound & Vision staged the first of its HDTV technology face-offs when we put a 37-inch Samsung plasma alongside a like-sized Sharp LCD, tuned them to the hilt, then fed them the same programs to see which was king of the HDTV hill ("Plasma vs. LCD," February/March 2005). In those days, flat-panel TVs were still an expensive oddity. But even then, the question "Which is better: plasma or LCD?" burned hard in the hearts of our enthusiast readers. Not surprisingly, that's now the No. 1 question we're asked about HDTV.

The results of that first battle were decisive. The Samsung plasma beat the Sharp LCD in virtually every key area, including contrast, color accuracy, picture uniformity, and picture detail. But much has changed. While plasma has continued to advance, set-makers have also worked hard to address LCD's most serious shortcomings. One of these is motion lag - obvious trails on moving objects created by the panel's relatively slow response time to the video signal. Another major issue is LCD's inability to reproduce deep blacks - a critical element for delivering natural, saturated colors and striking, lifelike contrast that adds depth and dimension to the image.

By early 2007, we began seeing LCDs that could finally hold a candle to the better plasmas. New panels with fast response times, coupled in some cases with 120-Hz screen-refresh circuitry (twice the conventional 60-Hz rate), have virtually eliminated motion lag. And throughout last year, contrast seemed to improve on every LCD we tested. But none of them, frankly, suggested that they had finally caught up enough to the best plasmas to warrant another side-by-side look. Until now.

The Technologies From the outside, flat-panel LCD and plasma displays look identical. But while the best of both breeds all have the 2 million or so pixels that constitute a "full HD" 1080p image, the similarities stop there.

Plasmas break those pixels into sealed red, green, and blue subpixels (or "cells") that contain an inert gas. When an electrical current - that is, a derivative of the video signal - excites the gas, it causes the colored phosphors in each subpixel to glow. By driving each subpixel to the desired level, the signal determines the pixel's exact color and brightness. Put enough of these pixels close enough together, and you get an image.

With an LCD (liquid-crystal display), a backlight - typically a fluorescent lamp - sits behind the pixel grid and shines through to the viewer. As with plasma, each pixel is broken into red, green, and blue subpixels, but the phosphors are replaced with colored filters. The video signal is processed to address each subpixel, causing its liquid-crystal structure to open and close like a shutter. This allows light to pass at the appropriate brightness and with the correct color to create the image.

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